Firewall definition

A security system that controls network traffic based on specified parameters. Firewalls prevent unauthorized access to secure internal systems by blocking potentially malicious activities from untrusted outside networks (like the internet).

Real firewall examples

• Windows Defender comes with a free firewall that is enabled by default on all Windows devices.
• macOS devices have their firewalls disabled by default, but they can be switched on in the Security & Privacy settings.

Watch it explained: Firewall and other terms

Further reading